July is here. In Chautauqua Lake, aquatic plants are growing abundantly, and algae is beginning to bloom. This lake is fed water and soils from a basin made of glacial soils with plenty of phosphorus, a primary nutrient fertilizing plants and algae which make this lake naturally productive with abundant fisheries. Lakes need a moderate number of aquatic plants and algae to support productive fisheries. As lakes age, they fill with sediments and nutrients delivered by tributaries, overland flow, and atmospheric deposition. However, human activity has accelerated this process, with much more phosphorus coming into the lake as part of the load of sediments, fertilizers, and human and animal waste than phosphorus leaving through lake’s outlet. The more that gets deposited, the more that’s available in future summers to feed the lake through “internal loading” from lake sediments. A 2012 report on Chautauqua Lake estimated that 75% of its phosphorus load came from external sources to the northern basin and 45% from external sources in the south basin.
Clearing watershed forests, and engaging in farming, transportation, and housing and commercial development fills lakes with excess nutrients and sediments. How much clearing and development can happen in a watershed before the receiving water experiences significant negative water quality and biological impacts?
Research indicates that waterways can tolerate the loss of up to 15-30% of their forest cover before measurably declining in quality. That translates to maintaining our contributing watersheds at a minimum of 70-85% forest and wetlands or suffer the consequences of the increased stormwater runoff, erosion, and loading of nutrients and sediments that come with suburbanization of lands. Chautauqua Lake’s watershed has a total forest and wetland cover of approximately 65%, below the optimal range. As more forest cover is lost, increasing amounts of stormwater, nutrients and sediments will impact lake tributaries and contribute to lake sedimentation and high phosphorus levels, promoting even more aquatic plant and algae growth.
Why does the conversion of forest to other land cover have such a detrimental impact on our streams and lakes? Forests are complex ecosystems working to capture and assimilate water and nutrients falling from the sky. When rain falls on a forest, the rain’s nutrients are largely absorbed by vegetation. If rain falls on a parking lot or rooftop, it often flows to the nearest ditch or storm drain to be conveyed directly to the lake, carrying its nutrients with it. If you compare a naturally forested lot to an identical residentially developed lot, you’ll find approximately five times the amount of stormwater runoff volume, seven times the phosphorus, and eighteen times the sediment on the developed lot! Every additional forest lot that is cleared in the watershed will incrementally and collectively add to the degradation of the lake. Converting only 5% of forested land to other uses could lead to a 40-50% increase in external phosphorus loading to the lake!
To slow the “aging” of our lake as much as possible, our county and its communities should establish a goal of no loss of wetlands and no net loss of forest lands in each lake watershed community to slow the degradation of Chautauqua Lake. This means: 1) permanently conserving as much remaining forests as possible, and 2) for every acre of forest developed, an acre of forest would have to be converted from lawn, commercial grounds, parking lot, or former farm field back to a natural forest environment. Enacting and enforcing stormwater laws must be done in addition to conservation. Such laws need to require that all new development and redevelopment or reconstruction of existing commercial and residential properties and parking lots reduce impervious surfaces and install stormwater capture and treatment systems, such as native landscaping, permeable paving, rain gardens, bioswales, and constructed wetlands, etc.
The Chautauqua Watershed Conservancy has prioritized landscapes across the region to target for conservation for water quality and habitat protection, including headwater forests, stream corridors, and wetlands. We’re working to communicate with the owners of the largest of these sites to explore conservation options and are seeking conservation investors and grants to help permanently protect these sites. Contact us at firstname.lastname@example.org if you’d like to help with these initiatives!
Article by John Jablonski III, Special Projects Coordinator
Image courtesy Wisconsin Dept. of Natural Resources